1. Field of the Invention
The invention relates to a method, a device and an arrangement for applying a reference mark on a rotor blade for a wind power plant, as well as to a use.
2. Description of Related Art
During operation of wind power plants, imbalances that arise due to differing settings of the rotor blade angles of the rotor blades of a rotor, lead to a reduction of the attainable energy yield. At the same time, these imbalances endanger the integrity of the wind power plant. Therefore, during setup and operation of wind power plants it must be ensured that the rotor blades of the wind power plant are operated with identical and predetermined adjustment angles. For this purpose, the rotor blades typically have reference marks, also called 0°-marks or zero marks, which are aligned with marks on the central rotor hub.
It has been shown in practice that faulty reference marks lead to rotor imbalances and reduced energy yield. If this is the case, the rotor blades must be recalibrated. An accuracy of at least 0.3° is required; however, an accuracy of less than 0.1° is preferable.
DE 196 28 073 C1 discloses a method for adjusting the blade angle of a wind power plant, according to which the power output of the wind power plant is measured time-resolved over a longer period of time. The power output is assigned to the power contributions of the individual rotor blades. The blade angles of the rotor blades are individually aligned and set in order to minimize differences of individual power contributions that arose, as well as aerodynamic imbalances. Thus, operational durability loads are reduced, and the excitation of a vibration resonant with the rotor speed is prevented.
DE 20 2007 008 066 U1 discloses a device for aligning an angle-adjustable rotor blade of a wind power plant that has at least two reference points which can be arranged in the interior of the rotor blade at predetermined positions to the rotor blade. The device comprises a measuring device with which the position of the reference points can be measured relative to a reference system. Placing the reference points in the interior of the rotor blade creates an option for measuring the rotor blade adjustment angles that is secure, accurate, time-saving and largely independent of the weather.
In a typical method for applying appropriate reference marks, an airfoil template is slid from the outside over a rotor blade, which is then calibrated by means of optical methods with respect to a reference plane, e.g., the rotor plane or the rotor axis plane. With current sizes of wind power plants having rotor diameters of far more than 100 m, applying such a template at over 50 m above the ground is a time consuming and costly measure.
For this reason, it is by now preferred to already provide the rotor blades with reference marks after their production, before they are mounted at a wind power plant. For this purpose, it is known that the position for a zero mark is measured on the outside at the root side end of a rotor blade using an unrolling measurement tape, starting from the separation plane of the rotor blade, i.e., the plane that separates an upper half shell from a lower half shell of the rotor blade. The half shells are typically composed of a composite of multiple layers of glass fiber mats and/or carbon fiber mats, laminated with a resin material.
Finally, jigs are also known which are positioned at the inner surfaces of the blade connection casings. In this method, the attainable accuracy depends on both the positioning accuracy of the casing in the flange, as well as the accuracy of the prior positioning of the flange on the rotor blade. These tolerances add up.
The necessary accuracy of 0.3°, preferably 0.1°, is not possible with the previously described methods because for the zero angle to be marked at the blade root, the tilt angle of the rotor blade in the power area is significant, that is, in the outer area arranged toward the tip of the rotor blade which yields the greatest power contribution at the rotor blade. Correspondingly, the 0° angle is defined relative to the leading edge of the rotor airfoil in the power region, relative to which the leading edge of the rotor airfoil at the blade root is rotated by a specific angle. Therefore, the zero mark in general does not correspond with the position of the airfoil leading edge at the blade root.
The rotor blade is very flexible and bends under its own weight. If the airfoil section or the airfoil leading edge in the power region is placed vertically, it is not guaranteed that the blade root side region is set relative to the former in a position or angular position reproducible to 0.1° to 0.3°. Due to individual tensions and distortions of each rotor blade, variations result in the angular relations and thus, in the reference mark points, which lie above the desired range of accuracy.
In contrast to this prior art, the object of the present invention is to be able to apply reference marks on a rotor blade for a wind power plant in a reproducible manner and with high accuracy.